OP, I can assure you that you have done nothing 'wrong' at all !
Yes, you have had a series of 'non' relationships, which have 'fizzled out', but that's not unusual at all.
The important thing to remember is that most 'relationships' gradually develop naturally. The fact that some of yours haven't doesn't mean anything other than you were not the right 'fit' for each other, that's all.
You could perhaps look at how fast you allow potential relationships to move forward, and whether you'd feel better if things moved at a slower pace ?
e.g You don't have sex with anyone until you've been seeing them for 2 months or that you don't take anyone to your home until you've known them for 3 months etc etc. But set a scale that you are comfortable with.
You could perhaps also 'weed out' the guys just looking for a 'fling' by discussing what you want out of a relationship, and not being 'shy' or 'awkward' about asking them what they are looking for too.
You shouldn't ever feel that you can't be open and honest about what you think, what you want, what you expect and what you need.
You'll find someone like minded, who will be worthy of your love, but in the meantime, just enjoy your dates, and never be afraid of being 'clingy' or 'needy'. You do have needs ! And if they can't meet them, then ''Next please !''